In the manufacture of complex machinery there is a need to produce parts on machine tools which have movement in more than three axes. This movement is generally in a simultaneous and coordinated mode made possible by the use of numerical control or computer direction. The usual arrangement for such a machine is with three orthogonal axes, X, Y, and Z, and one or two rotary axes, A and B. It is commonly found that this is accomplished by mounting the tool supporting spindle in a carrier which moves vertically with a saddle member (Y axis) that in turn is moved laterally and to and from the work along straight lines (X and Z axes, respectively) by its supporting structure. The spindle is supported in a yoke structure in the carrier for limited rotary motion around an A axis which is parallel to the X axis. It is common in such a machine when five axes are needed to place the B axis rotation mechanism under the workpiece support so that the workpiece rotates about the B axis which is parallel to the Y axis.
Machines such as the four and five axis configuration described have been equipped with automatic tool changers but in the execution of a tool change it has been the practice to swing the spindle about its A axis to a predetermined angular position relative to the saddle on which it is supported prior to the tool change. This then makes a tool change possible by fairly conventional mechanisms such as are known to be employed on less complex three axis machines. After the tool exchange the spindle is moved to the proper angular position to resume work.
Execution of the exchange of tools as described results in several disadvantages which have not previously been eliminated. The rotary motion of the spindle to the change position consumes substantial time and its return to a working angle thereafter compounds this problem with the result that there is an undesirable amount of time spent at each occurrence of a tool exchange.
Often the spindle must return with its new tool to the same angular position to complete machining of a particular angular surface thereon. The angular repeatability of the machine in this case must be exceptional and is very difficult to obtain. This results in a greatly increased costs during the building of such a machine.
In order to eliminate the disadvantages resulting from the return of the spindle to a predetermined angular position of the spindle, five axis machines have been developed which support the spindle for movement in only the X, Y and Z axis while the work is supported for motion around both the A and B axes. While this shortens tool change time and eliminates the angular repeatability problem, it introduces new problems that are difficult to solve. The programming of such a machine is more difficult and the overall space required for it is increased. Also the work is more remote from the solid base of the machine since it is supported on top of a stack including the two members rotating about the A and B axes and machine rigidity problems result.
It is therefore an object of this invention to provide a machine tool with a tool changer mechanism that will move tools to and from a spindle regardless of the A axis angular position of the spindle where that rotary axis of movement is built into the spindle supporting structure.